Phone-to-Phone Configuration for Internet Telephony

Internet telephony is promising for long-distance calls because of its low service charge and value-added functions. To use Internet telephony, a direct method is to use a computer connected to the Internet. However, non-Internet users constitute a significant portion of the general public, and Internet users may not be able to access the Internet at a certain time (e.g., when they are walking in the street or traveling in a bus without Internet access). To serve all users, a service provider can adopt the following phone-to-phone configuration: in each servicing city, a telephone gateway is used to bridge the local telephone network and the Internet, so that users can use telephones or mobile phones to access this telephone gateway for long-distance calls through the Internet. The phone-to-phone configuration involves two important issues:. (i)Service coverage: The service provider should provide service to many cities to attain good service coverage. However, it is costly to operate telephone gateways in many cities.(ii)Voice quality: Voice quality depends on various factors (e.g., coding method, available bandwidth, packet loss in the Internet, etc.). In the phone-to-phone configuration, multiple voice streams are sent from a source gateway to a destination gateway. This property can be exploited to tackle the packet loss problem for better voice quality. In this chapter, we describe the current methods for tackling the above two issues. Specifically, we describe the sparse telephone gateway configuration [Y.W. Leung, Sparse telephone gateway for Internet telephony, Comput. Netw. 54(1) (2010) 150-164.] which can serve many cities at lower cost, and describe the shared packet loss recovery method [Y.W. Leung, Shared packet loss recovery for Internet telephony, IEEE Commun. Lett. 9 (1) (2005) 84-86.] and the lightweight piggybacking method [W.Y. Chow, Y.W. Leung, Lightweight piggybacking for packet loss recovery in Internet telephony, Proceedings of the IEEE International Conference on Communications, Glasgow, UK, June 2007, pp. 1809-1814 (Revised version is under review by a journal.)], which exploit the property of the phone-to-phone configuration for effective packet loss recovery.